Protective relays are commonly used in electric utility applications to detect various possible problems in an electrical power system. Such relays protect a wide variety of equipment and are used in power systems, which also include circuit breakers. The primary function of a relay is to provide trip signals to circuit breakers.
Generally, current transformers and potential transformers are employed to obtain a signal in high current and/or high potential applications. Transformers reduce the magnitude of the current or voltage, and then feed the signal to the relays, meters and instruments at a much lower level for detection. The relay terminals may then be electrically connected to test switch terminals or poles. Test switches can be associated with one or more relays.
As is known in the art, it is necessary to short circuit the line and load terminals when the relay is removed from its case or the adjacent test switch is opened. The test switch provides this necessary short circuit or bypass feature. If this short circuit does not occur, the associated current transformer may be damaged and the safety of nearby personnel could be jeopardized. Voltage measurements can also be made directly on test switches, without disturbing existing connections.
Recent advancement in sensor technology has made it possible to replace conventional current transformers (“CT's”) and potential transformers (“PT's”) with current and voltage sensors, which deliver even lower levels of voltage signals. Because of this, it does not require the short circuit or bypass feature.
Terminals of the relay are connected to the transformers/sensors through a test switch, which includes connectors or terminals. Each test switch assembly can be associated with one or more relays. Test switches are designed with a housing that supports individual switches, also known as “poles”, and the rear terminals. The individual switches on the test switch assembly can be opened for the purposes of testing. In this manner, the test switch disconnects the protective relay from the sensors for the purposes of calibration and/or replacement. Thus, test switch assemblies are the means by which protective relays are taken out of service or isolated.
All measurements and tests can be performed at the front of the switchboard, without taking any devices out of service, and without the need to access wiring at the rear of the devices.
Test switches and test plugs have all the features necessary for applications involving the safe measurement and isolation of individual currents, voltages, and digital input/output (“I/O”) signals to facilitate testing of substation instrumentation and protection devices.
Technicians require access to the front and/or rear panels of the test switches to perform maintenance as well as troubleshoot after fault events occurring in the system. However, safely accessing the test switch panel necessitates that the technician determines the energized status of the conductors in the switch and the multiple power sources before beginning work. What is needed therefor is a test switch assembly that provides additional features to determine the status of the switches and the current and voltage transformers, as well as to reduce the need for specialized test equipment used during maintenance and troubleshooting. Therefore, there is a significant need for the unique apparatuses, methods, systems and techniques disclosed herein.